Fair Value Measurements and Marketable Securities - Marketable Securities with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, In loss position for less than twelve months, Fair Value	$ 20,437
Marketable securities, In loss position for less than twelve months, Unrealized Loss	(6)
U.S. Government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, In loss position for less than twelve months, Fair Value	3,002
Marketable securities, In loss position for less than twelve months, Unrealized Loss	(1)
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, In loss position for less than twelve months, Fair Value	17,435
Marketable securities, In loss position for less than twelve months, Unrealized Loss	$ (5)